1. Field of the Invention
The present invention relates to an antenna device that can be tuned to wide band frequencies.
2. Description of the Related Art
A known antenna device 10 is described with reference to FIGS. 4 and 5. A conductor 12 made of a fine metal wire is spirally wound around a ferrite magnetic core 14. Ends of the spiral conductor 12 form connection terminals 16 and 18. The spiral conductor 12 includes a plurality of divided conductor portions 12′, and the conductor portions 12′ are connected to one another by a plurality of capacitance elements 20. As shown in FIGS. 4 and 5, the antenna device 10 is such that the capacitance elements 20 are physically distributed in the spiral conductor 12 to have a closed loop form. The antenna device 10 responds to a particular frequency (see, for example, Japanese Unexamined Patent Application Publication No. 51-83755 (FIGS. 1 and 3) and its corresponding U.S. Pat. No. 3,946,397).
The known antenna device resonates with a particular frequency. Thus, when the known antenna device receives over wide bands, its reception sensitivity in frequencies other than the particular frequency decreases.